Polyester represented by polyethylene terephthalate (hereinafter referred to as “PET”) is widely used for fiber, a film, a resin, and the like due to its excellent mechanical strength, chemical resistance, and the like. For example, the fiber is widely used for industrial materials, for example, as a rubber reinforcement material such as a tire cord, a belt, a hose, and the like, as well as for medical applications.
Currently, among the polyester fiber for industrial materials, high strength polyester fiber including polyethylene terephthalate as a main component is widely used as a yarn for a seat belt. The yarn for a seat belt should, of course, maintain high strength, and it should also have good sliding efficiency after being manufactured into a seat belt so as to sharply decrease repeated friction with a sash guide, and friction generated when taking out and housing the seat belt for attachment and detachment.
As such, in order to impart sufficient sliding efficiency to polyester fiber for a seat belt, in general, an emulsion containing a lubricant is provided when preparing the polyester fiber. However, since polyester fiber for a seat belt is generally not colored, a dyeing process is required after weaving, and the lubricant-containing emulsion provided in the yarn preparing process may be eliminated during the dyeing process. For this reason, it is difficult to impart sufficient lubricity to polyester fiber for a seat belt by only providing a lubricant during a preparation process.
Further, in general, if conventional polyester fiber for a seat belt is subjected to processes of manufacturing a webbing product using yarn and dyeing it, the strength may be lowered due to high temperature heat treatment, and thus technology has been developed only toward increasing strength with high-strength yarn. Since yarn for a seat belt basically serves to fix a passenger to a car body upon a car accident, thereby reducing secondary damage, for the most important passenger protection it is very important to maintain strength of the yarn. However, if polyester fiber with a high modulus and low elongation at break is used for yarn for a seat belt, sliding efficiency for reducing friction generated when the seat belt is mounted in a vehicle and used may be significantly lowered, and it may cause injury to a passenger upon a car crash due to stiffness of the seat belt itself.
Accordingly, it is required to develop industrial high-strength polyester fiber used for a seat belt and the like which maintains excellent mechanical properties and high strength, and has significantly improved softness, abrasion resistance, strength retention, and the like to reduce impact on a passenger.